1. Field of the Invention
The invention relates to a smelting furnace system and a method for smelting metals, especially steel scrap, with a lower furnace vessel, in the bottom of which a tap hole is provided, and with an upper furnace vessel, which can be closed by a cover and in which a central pipe is provided coaxially with respect to the main axis of the furnase. A least one electrode is arranged, in the pipe and on the pipe there is provided a component which encompasses the upper furnace vessel and can be connected to a gas offtake device. The invention further relates to means for feeding the charge, a method for operating a smelting furnace system mentioned above and also a device for top blowing oxygen.
2. Discussion of the Prior Art
German reference DE-A-19 37 839 discloses a method and an arc furnace for the continuous smelting of iron scrap, in which the charging space in its upper part is separated from the combustion space of the furnace by a protective wall. In the lower part, the progressively slipping down slope of starting product is exposed to the radiation of the arc and the smelting product is discharged by known means arranged in the combustion space.
In the case of the furnace required for this purpose, the charge is passed only partly around the electrodes. In addition, the electrodes protrude from above through a cover into the smelting vessel.
German reference DE-B-23 42 959 discloses a shaft furnace in which the electrodes attached to a guide at the lower end are led through the charging pillar and the electrodes are kept at such a distance from the bottom of the shaft furnace that an approximately spherical melting space is formed.
The disadvantage of this device is that it is not possible for the length of the arc to be changed by moving the electrodes vertically, since the guide is held almost fixedly in the pillar of scrap.
Furthermore, German reference DE 42 36 510 C2 discloses a device for smelting scrap in which an arc furnace has a cathode protruding into a vessel of a shaft furnace operated on direct current. A cathode is provided at the bottom of the vessel. The anode is surrounded concentrically by a pipe and is movable in relation to said pipe.
In the case of this form of furnace, feeding of a charge from above over a large surface area onto the overall stock level is scarcely possible. Furthermore, in contrast to operating with three-phase current, in the case of the known shaft furnace the counter electrode has to be arranged in the bottom of the lower vessel, which leads to particular difficulties with respect to the service life of the lower furnace vessel.
The object of the invention is to provide by means of a simple design a smelting system with which a continuous smelting of metals, especially of scrap and of ores, is possible cost-effectively and which has as little environmental impact as possible.
The invention proposes a vessel which has a central pipe and a relatively high shaft. This arrangement makes it possible in a very reliable way to pass charges through the furnace in an annular form and at the same time preheat them by rising waste gases.
This vessel can be used as a smelting furnace which is run with electrodes operated on three-phase current. These electrodes are held by a supporting arm, which is led sideways through a sleeve and to which the central pipe is also fastened.
The electrodes are accommodated in a protected manner in the space inside the central pipe and protrude into the mouth region, the radiant heat melting the charge dropping down in an annular manner.
To boost the smelting capacity, burners may be used, operated by fossil combustion gases, for example natural gas. Furthermore, oxygen can also be blown in through these lances in the lower region.
Furthermore, the invention proposes introducing an oxygen lance into the central pipe. This oxygen lance has a supporting device of its own and can be moved independently of the electrode supporting arm. In an advantageous embodiment, this oxygen lance is moved from above centrally between the electrodes into the metallurgical vessel. In a further embodiment, the lance is bent by a bending device provided outside the furnace and is passed through the sleeve in a semicircular arc and positioned in such a way that its tip is exactly on the main axis of the furnace. The lance can be moved completely out of its position by simple means. When oxygen is used, the metallurgical vessel can be operated like a converter. Here it is thus possible to charge pig iron and at the same time low-carbon iron charge materials as well as the usual additions of lime and similar additives.
By simply switching off the oxygen supply and switching on the electrical energy, the metallurgical vessel can be changed over directly from converter operation to the operation of an electric arc furnace.
In an advantageous development, the central pipe is relatively far away from the bottom of the vessel in this operating mode.
During the later phase of introducing thermal energy via an electric arc, the central pipe is brought back close to the bottom and then serves both for guiding the charge and protecting the electrodes.